This project proposes to test the hypothesis that plasma membrane receptors specific for mannose-6-phosphate (M6P) serve to modulate the turnover of certain membrane components, either by anchoring lysosomal enzymes proximate to their cell surface substrates or by regulating the concentration of these enzymes in the extracellular fluid. We have obtained evidence that indicates the addition of M6P to human fibroblast culture alters the rate and pattern of turnover of 35SO4-labeled pericellular glycosaminoglycans (GAGs) into the extracellular compartment. We have also found that the addition of M6P results in changes in the polypeptide profiles of radioactive proteins released into the extracellular medium. We propose to continue this correlative study on the effect of M6P on the turnover of GAGs and proteins in cells with and without surface receptors for M6P, and in cells with and without lysosomal enzymes carrying the M6P marker. In addition, we wish to identify and characterize the molecular differences in GAGs and proteins derived from corresponding compartments of cultures treated with and without M6P. We also propose to test the possibility that radioactively-labeled proteins and GAGs of substrate-attached material can be digested and released into the medium by exogenously added cells and that this degradation process is sensitive to M6P. The successful achievement of these goals may allow us to establish assays for the purification of the enzyme(s) responsible for molecular differences observed in the proteins and GAGs of the cell surface and extracellular matrix as a result of M6P addition. These studies may provide insights on the role of lysosomal enzymes on the turnover of surface membrane components, on the general processes of cell adhesion to the substratum, cell movement, as well as certain diseased states such as osteoarthritis and metastasis.